(SUA)
A two-vessel cord represents a single umblical artery(SUA) assosiated with a number of fetal anomalies,but also is seen with much frequency as an isolated finding.
Images
Microscopic cross-section of a umbilical cord with a single artery. https://twitter.com/bansar_bansaria/status/862861717809876993
See also
anomalies of umbilical cord